Drilling wells through heaving or sloughing formations



March 12, 1940.

C. P. BOWlE El AL DRILLING WELLS THROUGH HEAVING 0R SLOUGHING FORMATIONS Filed Jan. 4, 1938 REFRIGERATOR (PUMP MUD CONDITIONER INVENTORS 1 M q-a WET-F, B0521 ATTORNEYS.

Patented Mar. 12, 1940 STATES PATENT DRILLING WELLS THROUGH HEAVING R SLOUGHING FORMATIONS Application January 4, 1938, Serial No. 183,294

6 Claims. (Cl. 255-1) OFFICE Our invention relates to the art of drilling wells and more especially to the art of drilling oil, gas, and water wells through formations that heave or slough into the hole.

In many parts of the world, as for example along the coast of the Gulf of Mexico in Texas, so-called heaving shales are encountered that do not stand up but heave or slough into the hole, often filling the hole as rapidly as it can be dug.

0 It is common practice to drill such holes with a mud fluid made by mixing a suitable clay with water. The hole is kept full of this fluid which is circulated by a pump down through the drill stem and rises between said stem and the walls of the hole, carrying to the surface the cuttings from the drill bit. The mud fluid by its weight and pressure, prevents the well from blowing in prematurely, by keeping back the flow of oil and gas. However, when this mud fluid encounters strata containing the so-called heaving materials it does not prevent them from caving but seems, on the contrary, to accelerate the caving. Often when the drill stem is withdrawn so that the drill bit, which has been dulled, may be replaced by a sharp bit, the sides of the hole will slough, sometimes filling the hole for a depth of 2000 feet above the bottom.

Practically all of the strata encountered in the earth's crust, when drilling wells, contain an appreciable amount of moisture. If this moisture can be frozen for a short distance into the formation surrounding the periphery of the well, the walls of the well will not slough or cave but will remain in a vertical position so long as the moisture in them is kept frozen.

The principalobject of our invention is to provide a fluid for drilling the well which not only will have the necessary weight to keep the well from blowing in prematurely, will act as a lubricant to the drill stem, and provide a means for carrying the cuttings to the surface, but will also freeze the sides and bottom of the hole as the drill proceeds and keep said sides and bottom frozen so long as circulation of the fluid is maintained.

To do this we substitute for the ordinary drilling fluid a brine made with the proper proportion of sodium chloride, calcium chloride, or other suitable material, that will make it possible to chill the brine to a temperature far below that necessary to freeze water and still have said brine sufliciently fluid so that it will circulate freely into and out of the well by means of pressure applied by a mud pump, or the drilling fluid may be any vehicle capable of removing heat from the formation. If desired, clay or other weighting material may be added to the brine to assist in making the fluid heavy enough to hold in the oil and gas pressure.

If the refrigerating fluid is of such nature that it will absorb or in any way interfere with the freezing of the moisture in the sides of the well, oil of a suitable gravity and viscosity may be used as the refrigerating fluid. Or an emulsion of oil and a suitable refrigerating fluid maybe made using oil of such surface tension that the refrigerant will consist of globules of the original refrigerating fluid surrounded by filaments of oil, thereby keeping the oil on the outside so that it and not the original refrigerating fluid will come in contact with the sides of the well. Or said emulsion may be made using a suitable fluid other than oil. Or a suitable compound may be added to said refrigerating fluid to prevent said refrigerating fluid from absorbing or in any way interfering with the freezing of the moisture in the walls of the well.

The brine, or other suitable vehicle, is preferably refrigerated on the surface in a refrigerating plant built for that purpose. It is chilled to the desired temperature and forced down through the drill stem by the mud pump, returning to the surface in the annular space between the drill stem and the casing, or the drill stem and periphery of the well. As the refrigerated fluid comes in contact with thesides and bottom of the well the moisture in the formation surrounding the well is frozen and as it returns to the surface it carries with it the cuttings from the drill. When it reaches the surface these outtings are removed by passing the fluid over a screen or shaker or other suitable device. The fluid isthen returned to the refrigerator where it is chilled to the desired temperature and recirculated to the well.

Some heaving or sloughing formations may be encountered which are dry, i. e. which do not contain sumcient moisture to permit them to be eflectively frozen. In such cases, the required amount of moisture may be supplied to the dry formation in any suitable manner and subsequently frozen. This can be accomplished by filling the well to a level above the dry formation with unrefrigerated water for a sufiicient length of time to allow it to permeate the dry formation, and then removing the water and circulating the refrigerated fluid in contact with the moistened formation as described above. Or if the dry sloughing formation is encountered while drilling with refrigerated fluid the refrigerating process is discontinued and unrefrigerated fluid is circulated through the well until the temperature of the fluid returning to the surface indicates that the temperature of the sides of the well, in the open hole below the casing, are above that of the freezing point of water, whereupon a slug of water is pumped into the well. When the walls have been sufflciently wetted, this slug of water is followed by the refrigerated fluid cooled to a desired temperature necessary to freeze the said water so that the walls, being reinforced by ice, will not cave or slough into the well.

The same process as described herein for freezing the water content of sloughing formations may be employed, if desired, for preventing sloughing of oil producing formations, or formations which contain any liquid capable of being congealed or solidified by low temperatures. In such cases, the character of the refrigerated fluid circulated through the well must be adapted to the character of the formation to be frozen, and it must be capable of itself remaining fluid at a temperature sufliciently low to oongeal or solidify the fluid content of the formation.

Some comparatively dry formations, particularly shales, are occasionally encountered, which do' not slough in their natural dry state, but

when supplied with additional moisture from the drilling mud, rapidly become unstable and slough off into the hole. In such formations, the use of an emulsion, as described hereinbefore, is particularly useful in that the emulsifying agent, whether oil or some other suitable film forming substance, prevents the liquid content of the emulsion from permeating the formation and causing it to slough. Under these conditions, it may be unnecessary to freeze the formation, the mere use of unrefrigerated emulsion as the drilling fluid being sufficient to prevent sloughing, by preserving the formation in a sumciently dry state.

For the last described use, a water and oil emulsion is satisfactory, the oil having suitable film forming qualities, and being used in such small amount as not to increase materially the cost of the driLing fluid, even if a porous stratum is reached, into which a considerable quantity of drilling fluid escapes.

Where the heaving formations occur at a known depth below the surface the portion of the hole from the surface to that depth may be drilled in the ordinary way, if desired, and the process herein described may be used for drilling through the heaving strata only; or, the herein described process may be used from the surface down.

The accompanying drawing is a diagram illus-' trating an arrangement of apparatus for carrying out the invention.

In the diagram, the reference numeral I designates a drill bit carried at the end of a hollow drill stem 2, said bit being operated in the usual manner to drill the well 3 through the earth formation 4. Mud fluid is forced by a pump 5 down through the drill stem 2, and rises in the space between said stem and the casing 5. The mud fluid is conditioned, i.'e. relieved of its burden of sand and cuttings from the drill bit and restored to its original condition, by suitable apparatus indicated at I, and is returned to the pump 5 for recirculation through the well. So much is common practise in the well drilling art.

When formation is encountered which has a tendency to heave or slough from the walls 8 of the hole, a brine or other suitable fluid or emulsion as described above is substituted for the ordinary mud fluid, and is circulated through the well in contact with the walls 8 thereof, by the pump. 5. If the formationis of the dry type described above, which sloughs only when additional moisture is supplied to it, an emulsion is used for the circulating fluid, and is pumped through the well at atmospheric temperature. sloughing is prevented by the failure of the emulsion to moisten the walls of the well.

If, however, the formation is of a type which sloughs naturally, and cannot be controlled merely by emulsifying the circulating fluid, said fluid,

which in this case may be any of those described herein, is chilled in a refrigerating apparatus S'before being pumped down into the well. to a temperature above its own freezing point but me.- terially lower than the freezing point of the formation fluid. This cold circulating fluid, rising through the well, freezes the fluid content of the formation for a short distance back from the walls of the. well, as indicated by the broken lines Ill. The frozen zone thus created in the formation immediately around the well prevents its sides 8 from heaving or sloughing. The well can be drilled, and the casing 6 set, without taking time to remove caved or sloughed material.

The circulating fluid may be used with or without the addition of clay to form a mud, according to the pressure and other conditions in the well. The essential characteristics of said fluid are that it must preserve the walls of the well and prevent sloughing therefrom, either by preventing moisture from permeating said walls, or by removing suflicient heat therefrom to freeze the natural moisture therein, and that it must be capable, either with or without the addition of clay, of performing the usual functions of drilling mud, i. e. of acting as a lubricant for the bit, as a vehicle for removing the cuttings, and as a seal to prevent the well from blowing in.

We claim:

1. The method of drilling wells through sloughing formation which consists in circulating refrigerating fluid through the well during the drilling thereof, said refrigerating fluid having a freezing point below the freezing point of the fluid content of the formation and functioning as a vehicle to carry off cuttings from the drill bit, and cooling said refrigerating fluid to a temperature'above its own freezing point but below the freezing point of said formation fluid, whereby the earth formation surrounding the well will be frozen.

2. The method of drilling wells to prevent sloughing which consists in circulating a brine through the well in contact with the walls thereof during the drilling operation, and cooling said brine to a temperature above its own freezing point but below the freezing point of water, whereby the earth formation surrounding the well will be frozen.

3. The method of drilling wells to prevent sloughing which consists in circulating mud laden fluid through the well in Contact with the walls thereof during the drilling operation, said mud fluid having a freezing point below that of water, and cooling said circulating fluid to a temperature above its own freezing point butv below the freezing point of water, whereby the earth formation surrounding the well will be frozen.

4. The method of drilling wells to prevent sloughing which consists in circulating an emulsion through the well in contact with the walls thereof during the drilling operation, said emulsion having a freezing point below that of water, and cooling said emulsion to a temperature above its own freezing point but below the freezing point of water, whereby the earth formation surrounding the well will be frozen.

5. The method of drilling wells to prevent sloughing which consists in causing fluid to flow into and through the well in contact with the walls thereof during the drilling operation, said fluid having a freezing point below that of water, and functioning as a vehicle to' carry off cuttings from the drill bit, recovering said fluid as it discharges from the well, removing the cuttings from said fluid, recirculating said fluid through the well, and cooling said fluid before it enters the well to a temperature above its own freezing point but below the freezing point of water, whereby water in the earth formation surrounding the well will be frozen.

6. The method of drilling wells through dry sloughing formation which consists in supplying water to the well to cause it to seep into said formation, then circulating through the well in contact with the moistened walls thereof a fluid at a temperature below the freezing point of water, whereby the formation surrounding the well will be frozen.

CLIFFORD P. BOWIE. RALPH V. HIGGINS. 

